The First Instar Larva of Hydrobius pauper SHARP (Coleoptera, Hydrophilidae)

Transcription

1 Elytra, Tokyo, New Series, 2 (2): December 31, 2012 title 279 The First Instar Larva of Hydrobius pauper SHARP (Coleoptera, Hydrophilidae) Yûsuke MINOSHIMA 1) & Masakazu HAYASHI 2) 1) Systematic Entomology, Graduate School of Agriculture, Hokkaido University, Sapporo, Japan m-yusuke@res.agr.hokudai.ac.jp 2) Hoshizaki Green Foundation, Okinoshima , Sono-chô, Izumo-shi, Shimane Pref., Japan hgf-haya@green-f.or.jp Abstract The first instar larva of Hydrobius pauper SHARP, 1884 is described. The larvae show intraspecific variation in the sclerotisation of the first maxillary palpomere which is usually incompletely sclerotised dorsally, but rarely the dorsal sclerotisation is complete, forming completely cylindrically sclerotised maxillary palpomere 1. The arrangement of mandibular sensilla MN1 3 of the first instar is shown to differ from larvae of the second and third instars. The thoracic and abdominal membranes of the first instar are without short pubescent tubercles, whereas the second and third ones bear short pubescent tubercles on the surfaces. Key words water scavenger beetle, Hydrophilinae, Hydrobiusini, larva, morphology, chaetotaxy Introduction After the publication of our study on the larval morphology of Hydrobius pauper SHARP, 1884 of the tribe Hydrobiusini (MINOSHIMA & HAYASHI, 2011), we had the opportunity to examine the first instar larva of the species and describe its morphology which has been unknown so far. We also provide short comments on the variation of two characters considered previously as invariable intraspecifically and used in previous studies (e.g., ARCHANGELSKY, 1997, 2004; MINOSHIMA & HAYASHI, 2011) as the taxonomically and phylogenetically important. Materials and Methods The methods follow those used by MINOSHIMA and HAYASHI (2011). The examined material is deposited in authors collections. We identified the larvae collected in the field by the comparing their morphology with that of second and third instars. Only single species of the genus Hydrobius, H. pauper, occurs in Japan and its second and third instar larvae were described by MINOSHIMA and HAYASHI (2011). Photographs were taken using a Pentax K-5 digital camera attached to an Olympus SZX12 stereoscopic microscope or a Zeiss Axiophot compound light microscope with a MeCan NY-1S digital SLR microscope adapter (MeCan Imaging Inc., Saitama, Japan), and subsequently adapted in Adobe Photoshop Lightroom 4 and Photoshop CS5. Composite images were created using the focus stacking software CombineZP (HADLEY, 2010). The morphology of the first instar larva is shortly compared with those of the second and third instars which were described by MINOSHIMA and HAYASHI (2011). Regarding the morphological terminology, we follow ARCHANGELSKY (1997) and MINOSHIMA and HAYASHI (2011) with the exception

2 280 Yûsuke MINOSHIMA & Masakazu HAYASHI of the antennal segments, for which we follow BEUTEL (1999) and FIKÁČEK et al. (2008); for the chaetotaxy of the larval head we refer to FIKÁČEK et al. (2008) and BYTTEBIER and TORRES (2009). Abbreviations are used as follows: AN: antenna; FR: frontale; gan: group of antennal sensilla; gapp: group of sensilla on the inner appendage of the maxilla; gfr: group of sensilla on the frontale; gla: group of sensilla on the labium; gmx: group of sensilla on the maxilla; L1: first instar larva; LA: labium; MN: mandible; MX: maxilla; PA: parietale; SE: sensorium. Description of Larva Hydrobius pauper SHARP, 1884 (Figs. 1 4) Material examined. 17 L1, Bibi-gawa River, Chitose-shi, Hokkaido, Japan, 29 VII 2011, M. HAYASHI leg. Additional description. General morphology. First instar. Colour. Head and sclerotised parts light yellowish brown; membranous parts slightly greyish white (Fig. 1). Head. Antenna (Fig. 3A B) rather stout. Antennomere 1 about as long as antennomere 2; antennomere 3 two-fifths as long as antennomere 2. Ventral surface of antennomere 2 bearing sparsely arranged small cuticular projections on inner part (Fig. 3B). Maxilla (Figs. 3E F, 4). Dorsal surface of intersegmental membrane between palpomeres 2 and 3 with a few small cuticular projections; palpomere 1 incompletely sclerotised cylindrically on dorsal surface (Figs. 3E, 4A B), but rarely, cylindrically sclerotised (Fig. 4C). Thorax and abdomen. Setation on sclerites of thoracic and abdominal segments sparser than those of the second and third instars. Dorsal and lateral surface of thoracic and abdominal membranes without small pubescent tubercles (this character was not mentioned in MINOSHIMA and HAYASHI (2011): the third instar larva bears densely arranged small pubescent tubercles on dorsal and lateral surface of thoracic and abdominal membrane; the second instar bears a few small pubescent tubercles on the surface). Primary chaetotaxy of head. Without additional sensilla, arrangement of primary sensilla closely similar to that of the second and third instars. Antenna (Fig. 3A B). AN6 on anterior third of sclerite. Mandible (Fig. 3C D). MN1 situated posterolaterally to MN2; MN2 between MN1 and MN3. Maxilla (Fig. 3E F). MX4 6 closely aggregated, situated lateroventrally on subapical portion of sclerite of stipes; MX5 located mesally to MX4 and MX6; MX4 posteriorly to MX6. Labium (Fig. 3G H). LA3 rather short seta, situated anteromesally to LA4. Discussion In our previous study of larval Hydrobiusini (MINOSHIMA & HAYASHI, 2011), we were able to examine only a restricted number of second and third instar larvae of Hydrobius pauper. In the present study, we examined 17 specimens of the first instar larvae of this species. The specimens show intraspecific variation of the sclerotisation of the first segment of the maxillary palpus (Figs. 3E, 4). The segment usually bears an incompletely sclerotised sclerite (its sclerotisation is interrupted dorsally; Figs. 3E, 4A B). In one out of 17 specimens examined, both dorsal portions of the sclerite are nar-

3 First Instar Larva of Hydrobius pauper 281 Fig. 1. Habitus of the first instar larva of Hydrobius pauper SHARP, 1884, dorsal and ventral view. rowly connected, and a completely sclerotised cylindrical sclerite is therefore present (Fig. 4C). The character, i.e., complete or incomplete dorsal sclerotisation of the palpomere 1, has been until now considered as a taxonomically and phylogenetically informative in the Hydrophilidae (e.g., ARCHAN- GELSKY, 1997, 2004; MINOSHIMA & HAYASHI, 2011). Our results suggest that multiple specimens should be examined in order to code this character properly in the future phylogenetic studies. The arrangement of the mandibular sensilla MN1 3 on first instar larva (Fig. 3C D) is different from those on the second and third instars (see MINOSHIMA & HAYASHI, 2011): the first instar larva has the seta MN1 situated more proximally than the pore MN3, whereas the second and third instars have the seta MN1 situated more distally than the pore MN3, the pore MN2 in all three instars is situated on the line connecting the sensilla MN1 and MN3. The arrangement is stable in the seven first instar larvae examined for this study in slide preparations. However we have examined only three second instar larvae and one third instar larva so far, and are therefore unable to exclude a possible variation of this character in higher instars. The same difference between the first and second plus third instars is

4 282 Yûsuke MINOSHIMA & Masakazu HAYASHI Fig. 2. Head capsule of Hydrobius pauper SHARP, 1884, first instar larva. A B, head capsule, dorsal (A) and ventral (B) view; C, detail of anterior margin of head capsule, dorsal view. also present in the European Hydrobius fuscipes (LINNAEUS, 1758) based on few larvae examined for this characters (M. FIKÁČEK, pers. comm., 2012). In addition to the above results, we confirm the homology of sensillum LA3 in this study, which was an ambiguously homologised sensillum on the basis of the study of the higher larval instars due to the present of a secondary seta (MINOSHIMA & HAYASHI, 2011: Fig. 47C). The sensillum LA3 is rather short seta which is presented anteromesally to LA4, therefore, the labial sensilla marked as 3? on the Figure 47C by MINOSHIMA and HAYASHI (2011) should be considered as LA3 sensillum.

5 First Instar Larva of Hydrobius pauper 283 Fig. 3. Head appendages of Hydrobius pauper SHARP, 1884, first instar larva. A B, antenna, dorsal (A) and ventral (B) view; C D, mandible, dorsal view; E F, maxilla, dorsal (E) and ventral (F) view; G H, labium, dorsal (G) and ventral (H) view. Fig. 4. Intraspecific variation of the first maxillary palpomere, first instar larva, dorsal view.

6 284 Yûsuke MINOSHIMA & Masakazu HAYASHI Acknowledgements We thank Masahiro ÔHARA (Hokkaido University Museum) for his kind advice and critical reading of the draft of the manuscript and Martin FIKÁČEK (National Museum, Prague, Czech Republic) for his critical reading and helpful comments on the manuscript, and for his personal comment of the arrangement of the mandibular sensilla of H. fuscipes; Miguel ARCHANGELSKY (CONICET-LIESA, Universidad Nacional de la Patagonia San Juan Bosco, Esquel, Argentine Republic) for his kind advices. This study was partly supported by Grant-in-Aid for JSPS Fellows (10J03421) to Y. MINO- SHIMA. 要 約 Hydrobius pauper SHARP (MINOSHIMA & HAYASHI, 2011) MN1 3 MINOSHIMA and HAYASHI (2011) MINOSHIMA and HAYASHI (2011) LA3 MINOSHIMA and HAYASHI (2011) LA3? LA3 References ARCHANGELSKY, M., Studies on the biology, ecology, and systematics of the immature stages of New World Hydrophiloidea (Coleoptera: Staphyliniformia). Bull. Ohio biol. Surv., (n. ser.), 12: Higher-level phylogeny of Hydrophilinae (Coleoptera: Hydrophilidae) based on larval, pupal and adult characters. Syst. Ent., 29(2): BEUTEL, R. G., Morphology and evolution of the larval head of Hydrophiloidea and Histeroidea (Coleoptera: Staphyliniformia). Tijdschr. Ent., 142: BYTTEBIER, B., & P. L. M. TORRES, Description of the preimaginal stages of Enochrus (Hugoscottia) variegatus (STEINHEIL, 1869) and E. (Methydrus) vulgaris (STEINHEIL, 1869) (Coleoptera: Hydrophilidae), with emphasis on larval morphometry and chaetotaxy. Zootaxa, Auckland, 2139: FIKÁČEK, M., M. ARCHANGELSKY & P. L. M. TORRES, Primary chaetotaxy of the larval head capsule and head appendages of the Hydrophilidae (Coleoptera) based on larva of Hydrobius fuscipes (LINNAEUS, 1758). Ibid., 1874: HADLEY, A., CombineZP (6th of June 2010). [Available online at LINNAEUS, C., Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata pp. Holmiæ, Laurentii Salvii. MINOSHIMA, Y., & M. HAYASHI, Larval morphology of the Japanese species of the tribes Acidocerini, Hydrobiusini and Hydrophilini (Coleoptera: Hydrophilidae). Acta ent. Mus. nat., Pragae, 51 (supplementum): SHARP, D., The water-beetles of Japan. Trans. ent. Soc., London, 1884: Manuscript received 10 October 2012; revised and accepted 10 November 2012